Action: Remove or control fish by drying out ponds
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- One before-and-after study in the USA found that draining ponds to eliminate fish increased numbers of amphibian species. One replicated, before-and-after study in Estonia found that pond restoration, which sometimes included drying to eliminate fish, and pond creation increased numbers of species and breeding populations of common spadefoot toads and great crested newts compared to no management.
- Three studies (including one review) in the UK and USA found that pond drying to eliminate fish, along with other management activities in some cases, increased breeding success of frog or newt species.
Occasional drying of ponds can help control predators including native or non-native fish species.
Supporting evidence from individual studies
A before-and-after study in 1986–1995 of a pond within a housing development near Peterborough, England, UK (Cooke 1997) found that fish removal by pond drying, along with pond deepening, maintained populations of great crested newts Triturus cristatus and smooth newts Triturus vulgaris seven years after the development. Larval catches increased the year after fish removal (crested: 37; smooth: 13) and then varied (crested: 1–14; smooth: 1–22). Although adults of both species reproduced after the development (crested: 41–102; smooth: 7–68), production of metamorphs failed in 1990 due to introduction of three-spined sticklebacks Gasterosteus aculeatus. Development was undertaken in 1987–1989. The pond (800 m2) was deepened in 1988 and fish were removed by pond drying in 1990. A 1 ha area was retained around the pond. Newts were counted by torch and larvae netted once or twice in 1986–1987 and 3–4 times in March–May 1988–1995.
A review of fish control programmes from 1992 to 2001 at a pond in England, Australia and Alabama, USA (Watson 2002) found that breeding success increased for two frog species following pond draining. At the Australian site, green and golden bell frogs Litoria aurea bred successfully the year after a reduction of non-native plague minnows Gambusia holbrooki. In Alabama, breeding success of dusky gopher frogs Rana capito sevosa increased following draining and rotenone treatment (egg masses: 10 to 150). In England, one great crested newt Triturus cristatus colonized a pond in the first year following elimination of sticklebacks (Gasterosteidae). A pond (690 m2) in England was drained down to 20 cm and bottom sediments agitated to release gases in 2001. A pond on Kooragang Island, Australia was drained in 1997. A pond in Alabama was drained, fish removed and then rotenone added in 1992.
A replicated, before-and-after study in 1998–2003 of seven ponds in California, USA (Alvarez, Dunn & Zuur 2002/2003) found that the reproductive success of California red-legged frogs Rana draytonii increased significantly following elimination of non-native fish by pond drying. Adult numbers were similar after fish elimination (0–40 to 1–41/pond), but juveniles increased significantly (0–15 to 1–650). Fish were eliminated during the first draining, or for two ponds with mosquitofish Gambusia affinis on the second draining. Seven ponds were drained in autumn in 1998–2001. Pumps were used to drain the water to a depth of 50 cm and then below 3 cm. Seines, throw nets and dip nets were used to remove all fish. Mud was smoothed and a small amount of household bleach applied to eliminate mosquitofish. Ponds were filled from ground water springs. Red-legged frogs and fish were surveyed six times per year in 1998–2001.
A before-and-after study in 1999–2001 of a seasonal wetland bay in South Carolina, USA (Scott, Metts & Whitfield Gibbons 2008) found that removing fish by drying the bay increased amphibian species richness. Before removal the bay supported only cricket frogs Acris gryllus. After fish removal the bay supported nine amphibian species including the Carolina gopher frog Rana capito. Amphibians were sampled in 1999 before fish removal and in the spring of 2001.
A replicated, before-and-after site comparison study of 450 existing ponds, 22 of which were restored, and 208 created ponds in six protected areas in Estonia (Rannap, Lõhmus & Briggs 2009) found that within three years amphibian species richness was higher in both restored ponds, some of which had been drained to eliminate fish, and created ponds than unmanaged ponds (3 vs 2 species/pond). The proportion of ponds occupied also increased for targeted common spadefoot toad Pelobates fuscus (2 to 15%) and great crested newt Triturus cristatus (24 to 71%), as well as the other five species present (15–58% to 41–82%). Breeding occurred at increasing numbers of pond clusters from one to three years after restoration/creation for crested newt (39% to 92%) and spadefoot toad (30% to 81%). Prior to management, only 22% of ponds were considered high quality for breeding. In 2005, 405 existing ponds were sampled by dip-netting. In autumn 2005–2007, ponds were restored and created for great crested newts and spadefoot toads in 27 clusters. Restoration included clearing vegetation, extracting mud, levelled banks and for fish elimination pond drying and ditch blocking. Post-restoration monitoring in 2006–2008 comprised an annual visual count and dip-netting survey.
- Cooke A.S. (1997) Monitoring a breeding population of crested newts (Triturus cristatus) in a housing development. Herpetological Journal, 7, 37-41
- Watson W.R.C. (2002) Review of fish control methods for the great crested newt species action plan. Countryside Council for Wales Contract Science Report No 476. Countryside Council for Wales report.
- Alvarez J.A., Dunn C. & Zuur A.F. (2002) Response of California red-legged frogs to removal of non-native fish. Transactions of the western section of the Wildlife Society, 38/39, 9-12
- Scott D.E., Metts B.S. & Whitfield Gibbons J. (2008) Enhancing amphibian biodiversity on golf courses with seasonal wetlands. Pages 285-292 in: Urban Herpetology. SSAR, Salt Lake City.
- Rannap R., Lõhmus A. & Briggs L. (2009) Restoring ponds for amphibians: a success story. Hydrobiologia, 634, 87-95